Positive earth

[iannuls]

QUESTION

I have been reading all I can about positive earth. I still don't understand. Can anyone explain in laymans terms what is the point of positive earth (Someone said it provides corrosion protection - true?). Were all pre 60's cars positive earth? I want to hook up the starter once I get a carb on, but my only experience is with negative earthed cars.

I will have to rewire the thing eventually, as the wiring looks very crook (And has been pretty butchered by the guy who stripped the chassis), should I think about changing to a negative earth?

The existing wiring is plastic, would that be original, or was it originally fabric wiring? I know new plastic negative earth wouldn't be absolutely original, but I want a reliable useable S1. Do people generally retrofit fuses to protect their wiring?

Cheers

PS I have read a few threads on polarity, but they get very technical, very quickly.

Ian

1956 S1 86"

[Scouse]

I believe the original point of +ve earth was to help prevent spark plug electrode erosion. How true that is, I don't know.

The wiring for -ve & +ve earth is virtually all the same (battery cables are the exception but generally left as is anyway).

99.9% of +ve earthed cars have been changed over to -ve due to most accessories being designed for the -ve earth system.

In my experience, fabric wiring gave way to plastic in the mid-late 1950s. I would spend a few $ & get a new harness.

All your original parts (starter, wiper, generator, fuel pump) will work either way.

[JDNSW]

The point of positive earth is that as Scouse says, it gives a better spark.

To quote from S.P.Smith, "The Electrical Equipment of Automobiles", 1945:-
"The sparking voltage is controlled by the temperature of the negative electrode....the voltage is lower when the centre electrode is negative."
also ""corrosion is usually less when the positive terminal is earthed".

There has never been complete standardisation, but by 1937 most cars had positive earth. In the 1960s, transistor car radios started to be used for car radios, and early transistors mandated a circuit with the earth negative. This led to a gradual changeover to negative earth - even though radio circuits could be (and were) designed to work with either polarity, negative earth ones became standard, as they were cheaper to build. This resulted in almost all cars having changed to negative earth by the end of the 1960s. The change was really quite rapid. Similar reasons led to the complete change from six to twelve volts, which had already happened before WW2 for most manufacturers except in the USA. Just about the last holdout on the Australian scene was VW - Holden changed in about 1960 I think.

Polarity can be easily changed on Landrovers with generators simply by reversing the battery connections and momentarily shorting the cutout in the voltage regulator to give some remnant polarisation the right way. The only other change needed is to reverse the connections to the ammeter. But if there is contemporary car radio or other electronic equipment fitted, make sure you understand its polarity requirements, as it is likely to be damaged if wrong polarity is applied!

If it has been changed to an alternator, it is almost certainly already negative earth, as positive earth alternators are extremely rare.

John

[101RRS]

Polarity can be easily changed on Landrovers with generators simply by reversing the battery connections and momentarily shorting the cutout in the voltage regulator to give some remnant polarisation the right way.

John

When I bought my 88 basic the battery was connected, negative to earth. After a while I noticed the amp was always showing discharge and thought the generator was not working.

Later, on a whim, I changed the battery to make things positive earth - everything started and ran OK and even the ammeter was now showing positive charge - the starter motor even turned the right way. I didn't short the cutout on the voltage regulator so even this action may not be needed.

Cheers

Garry

[Aaron IIA]

the starter motor even turned the right way. I didn't short the cutout on the voltage regulator so even this action may not be needed.


The starter motor is series wound, so polarity will make no difference to it's operation. If you have a charge indicator light, you may not have to re-polarise the generator. If you do not have a charge indicator light, you will have to re-polarise the generator.

Aaron.

[Scouse]

I didn't short the cutout on the voltage regulator so even this action may not be needed.

Sometimes you don't need to. If you're game, give the engine a rev & the warning light will go very bright for a second. Then it will go out & everything will be good.

Chances are that you won't find that's a generally acceptable practice though :D.

[101RRS]

Sometimes you don't need to. If you're game, give the engine a rev & the warning light will go very bright for a second. Then it will go out & everything will be good.

Chances are that you won't find that's a generally acceptable practice though :D.

Ignorance is bliss :D

[dennisS1]

This is an old point of contention, there are all sorts of arguments about which is better, corrosion may be a point, spark plug life may also be right but remember over the last 100 years there has been more than one theory about flow direction of electrons (current) any way. As I remember most early and right up to the 70s care radios had a polarity switch on them as there were a lot of positive earth cars.
Now down to the practicality I have 4 registered S1 all are Pos to earth because that’s the way they should be. This does not present as big a problem as you may think; you can still charge your phone, run your navigator, car fridge or any other device that does not have a live chassis. I have UHF in 2 but they are Phillips units, a HF again no live chassis. Yes a 16 channel sound system is out but you won’t hear it anyway.
If you buy a new loom buy a fabric covered one it will cost about the same but will look heaps better and remember the first one lasted 60 years. It is right that all the standard equipment will work both ways but the Generator should be re-polarised, change the coil and amp meter.
Dennis

[JDNSW]

............, change the coil and amp meter.
Dennis

Whether changing the coil is a good or bad idea depends on how it is wound - whether the secondary is connected to the frame or the primary. If the latter, the connections should not be changed, but in any case you are unlikely to see any difference either way.

John

[series1buff]

I recall reading that modern cars ( post 70's ) with NEG ground systems ..have the coil wound and connected in such a way as to produce a NEG voltage at the spark plug centre electrode . Sounds weird , but thats what I read. If you reverse the coil connections , you will lose around %10 of spark energy .

Ive also read about the prevention of distributor points surface erosion by having a + ground ststem ....

There was a certain make of US cars in the 40's that had a switched + to - system :each time you pressed the floor starter ...an elaborate switch changed the dissy points from + to - polarity ..and back again ... to reduce point surface degredation..

Mike

[Aaron IIA]

Ive also read about the prevention of distributor points surface erosion by having a + ground ststem ....

There was a certain make of US cars in the 40's that had a switched + to - system :each time you pressed the floor starter ...an elaborate switch changed the dissy points from + to - polarity ..and back again ... to reduce point surface degredation..

Having the corect condensor, tuned to the coil, will greatly improve the points condition.

Aaron.

[iannuls]

I tend to agree (+ve earth is more original and fabric wiring looks better and costs much the same for a loom (Where's best to get it by the way)) What's left of the wiring on my S1 is -ve earth plastic, so must be a more recent replacement and my donor vehicle is plastic -ve earth spaghetti conversion, so I don't have much to go on to see what original wiring looks like. Anyone got any good close up +ve wiring pics?

Ian

1956 S1 "86